<template>
    <ul class="list">
        <li class="item" 
            v-for="item in letters"
            :key="item"
            :ref="item"
            @touchstart.prevent="handleTouchStart"
            @touchmove="handleTouchMove"
            @touchend="handleTouchEnd"
            @click="handleLetterClick"
        >
            {{item}}
        </li>
    </ul>
</template>

<script>
export default {
    name:'CityAlphabet',
    props:{
        cities:Object
    },
    data(){
        return{
            touchStatus:false,
            startY : 0,
            timer:null
        }
    },
    updated(){
        this.startY = this.$refs['A'][0].offsetTop
    },
    computed:{
        letters(){
            const letters = []
            for(let i in this.cities){
                letters.push(i)
            }
            return letters
        }
    },
    methods:{
        handleLetterClick(e){
            this.$emit('change',e.target.innerText)
        },
        handleTouchStart(e){
            this.touchStatus = true
        },
        handleTouchMove(e){
            if(this.timer){
                clearTimeout(this.timer)
            }
            this.timer = setTimeout(()=>{
                    if(this.touchStatus){
                    const touchY = e.touches[0].clientY - 79
                    const index = Math.floor((touchY-this.startY)/23)
                    if(index>=0 && index<this.letters.length){
                        this.$emit('change',this.letters[index])
                    }
                }
            },8)
        },
        handleTouchEnd(){
            this.touchStatus = false
        }
    }
}
</script>

<style lang="stylus" scoped>
    @import '~styles/varibles.styl';
    .list
        display: flex
        flex-direction: column
        justify-content: center
        position: absolute
        right:0
        top:1.58rem
        bottom:0
        width 0.4rem
        .item
            text-align: center
            line-height: .46rem
            color:$bgColor
            font-weight: bold
</style>